BUG: Decref `loadtxt` converters when done
BUG: Decref `loadtxt` converters when done

Possibly they were just not incref'd in an earlier version of the
code.  But incref'ing seems right, so this adds the proper decref
loop.

mhvk/numpy,anntzer/numpy,endolith/numpy,mhvk/numpy,rgommers/numpy,pdebuyl/numpy,mhvk/numpy,numpy/numpy,rgommers/numpy,endolith/numpy,anntzer/numpy,pdebuyl/numpy,anntzer/numpy,mattip/numpy,numpy/numpy,mattip/numpy,charris/numpy,charris/numpy,endolith/numpy,mattip/numpy,anntzer/numpy,numpy/numpy,rgommers/numpy,endolith/numpy,mattip/numpy,mhvk/numpy,charris/numpy,numpy/numpy,pdebuyl/numpy,rgommers/numpy,mhvk/numpy,charris/numpy,pdebuyl/numpy